This inventions based on and claims priority to Japanese Patent Application No. Hei 11-186192, filed Jun. 30, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a marine drive transmission, and more particularly to an improved marine drive transmission that absorbs a shift shock.
2. Description of Related Art
A wide variety of marine propulsion units propel watercraft. For instance, outboard motors commonly power boats and other watercraft. Stern drive units, which include an inboard motor and an outboard drive, also are often used to power boats and watercraft.
A typical outboard motor includes a power head atop a drive unit. The power head includes an internal combustion engine having an output shaft extending generally vertically. A driveshaft housing depends from the power head and encloses a driveshaft that extends generally vertically from the output shaft. A lower unit further depends from the driveshaft housing. A propulsion shaft is provided therein and extends generally horizontally. The driveshaft and the propulsion shaft are coupled together within the lower unit so that the propulsion shaft extends normal to the driveshaft. A propulsion device, such as, for example, a propeller is affixed to an outer end of the propulsion shaft. A bevel gear transmission, for example, is provided between the driveshaft and the propulsion shaft and includes a forward, neutral, reverse shift mechanism for moving between forward, neutral and reverse positions. The engine powers the propeller through the driveshaft, bevel gear transmission and propulsion shaft. The propeller, thus, can propel the outboard motor and the associated watercraft in both forward and reverse directions, unless the shift mechanism is in the neutral position.
An outboard section of the stem drive unit has a construction similar to that of the outboard motor except that the engine is not positioned over the propulsion device. The engine is placed in the hull of the watercraft. A propulsion device of the stern drive unit, which typically is a propeller, is powered by the engine through the driveshaft and propulsion shaft combination (i.e., drive train arrangement) similar to that of the drive unit of the outboard motor.
Users continue to desire more powerful marine drives and prefer large propulsion units having engines which produce higher horsepower. An engine, for example, which operates on a four-stroke combustion principle and having multiple cylinders, can provide the desired increased horsepower.
However, when engaging these larger engines, the marine propulsion unit tends to jolt the occupants of the watercraft. The sudden movement gives the occupants an uncomfortable feeling. In other words, because the large-sized engine generates a relatively strong propulsive force, an uncomfortable shock is created by the abrupt change in direction of the propulsive force, particularly when the shift mechanism is shifted from the neutral position to the forward drive position or to the reverse drive position.
In order to address this problem, a shock absorbing device for the shift mechanism has been proposed in U.S. Pat. No. 4,747,796. FIGS. 1 and 2 illustrate this type of coupling. FIG. 1 is a cross-sectional, side elevational view of a transmission coupling 20 arranged to absorb the shock, and FIG. 2 is a cross-sectional view of the coupling 20 taken along the line 2xe2x80x942 of FIG. 1.
With reference to these figures, a driveshaft 22 is divided into a drive section 24 and a driven section 26 and the coupling 20 joins these sections. The lower end of the drive section 24 has a depending socket 28 that defines an internal cavity 30. An upper end portion 32 of the driven section 26 extends into the cavity 30. Three blocks of elastic members 34 are interposed between the internal cavity 30 and the end portion 32. As seen in FIG. 2, the socket 28 and its internal cavity 30 have a generally triangular configuration in section. The end portion 32 has a complementary triangular shape featuring three points 38.
The coupling 20 provides vibration damping and force absorption under a low speed and low load condition. This damping is provided by the compressible elastic members 34. When the driving load increases, the elastic members 34 are increasingly compressed and the points 38 of the projecting portion 32 directly contact the inner cavity 30 of the socket 28. The torque of the drive section 24 is transmitted to the driven section 26 through this connection.
Because the transmission shift shock occurs under low speeds, the coupling 20 is quite useful for preventing the shock. However, another problem arises with this coupling 20, namely, the driving force cannot be securely transferred from the drive section 24 to the driven section 26 when the driving load increases, because the driving force is conveyed to the inner cavity 30 by the contacts of the points 38 and these contacts are unreliable. Of course, the elastic members 34 also are involved in this force transferring mechanism; however, the elastic members 34 tend to slip within the cavity 30 and do not increase reliability.
Increasing the contact areas between the points 38 and the cavity 30 or using elastic members that have larger volumes could resolve the above-identified problems. Both of the improvements, however, would require enlarging the surrounding housing and would thereby interfere with the arrangement of other components disposed proximate the housing.
A need therefore exists for a marine drive transmission that can absorb a shock generated when a shift mechanism is operated. The transmission preferably has a compact structure comprising a coupling that can securely transmit the driving force from a drive section to a driven section after operation of the shift mechanism.
In accordance with one aspect of the present invention, a power transmission system for a marine propulsion unit is provided. The marine propulsion unit has a powering element and a propulsion device. The power transmission system comprises a first shaft driven by the powering element, and a second shaft driven by the first shaft and driving the propulsion device. The first and second shafts have a common axis. A coupling assembly is mounted on both the first and second shafts so as to couple the first and second shafts for rotation together. A damper is disposed next to the coupling assembly. The coupling assembly includes a pair. of coupling members. One of the coupling members is axially moveable along the common axis relative to the other coupling member to compress the damper at the moment the first shaft begins to drive the second shaft.
In accordance with another aspect of the present invention, a coupling for a power transmission is provided. The power transmission has a drive shaft and a driven shaft. The coupling comprises a first member. The first member is rotatable together with one of the drive shaft and the driven shaft and has at least one tooth extending axially. The coupling comprises also a second member. The second member is rotatable together with the other shaft and has at least one tooth extending axially to engage with the tooth of the first member. A damper is disposed next to the second member. Confinement members confine the first member, second member and the damper therebetween. The second member compresses the dampers when the drive shaft begins to rotate the driven shaft.
In accordance with a further aspect of the present invention, a marine drive comprises a shaft. The shaft includes a first section driven by a prime mover and a second section driven by the first section to drive a propulsion mechanism. A first coupling member is connected to one of the first and second sections by spline connection. A second coupling member is connected to the other section by spline connection. Both the first and second coupling members are coupled with each other. A shock absorber is disposed adjacent to the second coupling member. The second coupling member bumps into the shock absorber when the first section starts rotating the second section that has been at a standstill.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.